1. Field of the Invention
The present invention generally relates to a mobile communication system, and in particular, to a method of reporting a channel state in a mobile communication system.
2. Description of the Related Art
In a 4th-Generation (4G) mobile communication system, which is the next generation communication system, research has been actively pursued to provide users with services at a high transmission rate of about 100 Mbps.
Adaptive Modulation and Coding (AMC) is a scheme for high-speed data transmission. The AMC scheme determines different modulation schemes and coding schemes according to channel states between a Base Station (BS) and a Mobile Station (MS), thereby improving overall system efficiency. The AMC scheme having a plurality of modulation schemes and a plurality of coding schemes modulates and codes channel signals using combinations of the modulation schemes and the coding schemes.
Generally, each of the combinations of the modulation schemes and the coding schemes is referred to as a Modulation and Coding Scheme (MCS) and a plurality of MCSs from level 1 to level N can be defined according to the number of the MCSs. In other words, the AMC scheme adaptively determines the MCS level according to the channel states between the MS and the BS, thereby improving overall system efficiency.
In a mobile communication system using the AMC scheme, an MS periodically measures the channel state of a downlink and transmits information about the measured channel state, i.e., Channel State Information (CSI), to a BS and the BS determines one of the MCS levels based on the CSI received from the MS. The BS transmits data according to the determined MCS level.
However, according to the AMC scheme, the MS has to periodically transmit CSI to the BS, increasing signaling overhead. Moreover, the MS reports a Carrier-to-Interference and Noise Ratio (CINR) or a Received Signal Strength Indicator (RSSI) to the BS. Such a channel state report does not reflect a correct channel state.